The invention relates generally to a method and apparatus for blade sharpening. More specifically, the invention provides a method and apparatus for sharpening rotary law mover blades and, in particular, sharpening both clockwise rotating and counter-clockwise rotating blades as well as sharpening both standard and mulching type lawnmower blades.
As civilization has progressed from its primeval beginnings, small groups of people formed mobile communities that worked together to hunt and gather food for themselves. As their knowledge and technology advanced, they became more settled and found ways to cultivate the earth and domesticate animals for their own use and benefit without the need to be constantly on the move. As civilizations advanced further, these groups became larger communities and even large cities for trade, commerce and other activities. These activities generated greater wealth for some individuals such that they could own their own homes and have servants to take care of many, if not all, of the domestic chores such as, but not limited to, washing clothes, cleaning the household, caring for the children, preparing and cleaning up meals and so forth. At some point in time, the exact date being unknown, wealthy home owners decided to hire servants to tend the household yards in order to make more enjoyable use of the property they owned. One of the tasks required to tend the yards was to keep the lawn mowed in a neat and pleasing appearance. At that time, the process for mowing the lawns consisted of hiring a group of servants with hand sickles to cut the lawn by hand. As would be apparent to anyone considering this activity, it was a constant and laborious task to accomplish.
With more advances in technology came manual hand powered lawnmowers and later gasoline powered lawnmowers. It is only in recent history that riding lawnmowers have become available for property owners personal use. While these obvious advances are plain for most individuals to see and appreciate, there have been many more advances that most people are unaware of or take no notice of. These advances include such things as a better means for leveling a power lawnmower desk so as to provide a more even appearance to a cut lawn. Wide, low air pressure filled tires allow a lawn tractor to traverse over most ground surfaces without leaving tire marks in the ground or grass. A better understanding of how to properly cut grass led to a better understanding of the proper blade cutting edge and angle that a lawnmower blade should have. A further advancement was the development of an automatic means for collecting the grass clippings and debris as the lawn was being mowed, typically known as a bagger. This allowed for easy disposal of the clippings and debris and greatly reduced the time for yard maintenance.
As an alternative to collecting the grass clippings and disposing of them, came the development of what is known in the art as mulching lawnmower blades. Mulching lawnmower blades cut the grass into much smaller pieces which, when left back on the ground, decompose quickly and leave their nutrients back into the soil to aid in the growth of new grass. A standard, or non-mulching, clockwise rotating lawnmower blade 1, as shown in FIG. 1, has two (2) primary cutting edges 2 and 3 that are on the same horizontal plane. There is a mounting hole 4 at the center of the blade 1 for mounting the lawn mower blade 1 to a driven shaft (not shown). A mulching clockwise rotating lawnmower blade 6, as shown in FIG. 2, has four (4) cutting edges along with a mounting hole 4. The lower two cutting edges are the primary cutting edges 2 and 3 and lie on a first horizontal plane. The top two cutting edges are secondary cutting edges 7 and 8 and lie on a second horizontal plane above the first horizontal plane. Both the standard clockwise rotating blade 1 and the mulching type clockwise rotating blade 6 have upturned ends 5 of the non-cutting primary edges which causes the cut grass to be lifted upwards above the blade 1 or 6. With a mulching type lawnmower blade 6, as the grass is cut for a first time with the primary cutting edges 2 and 3, the portion of grass that was cut off is lifted by air pressure created by the rotating mulching lawnmower blade 6 and the upturned ends 5 such that the cut off portion of grass encounters the secondary cutting edges 7 and 8 which further cuts the grass portion into finer bits of grass for quicker decomposition.
For many people, the use of mulching type lawnmower blades 6 is a preferable alternative as there is no need to spend time and effort to collect and then dispose of the grass clippings and it has the further advantage of returning the nutrients back into the soil for further plant growth.
In addition to the standard clockwise rotating lawnmower blade 1 and the mulching type clockwise rotating lawnmower blade 6, there are also two categories that define the type of lawnmower blade that is utilized in lawnmowers. These are the clockwise rotating lawnmower blades 1 or 6 and the counter-clockwise rotating lawnmower blades 9, of which only the standard blade 9 is shown in FIG. 3. FIG. 1 depicts a standard clockwise rotating lawnmower blade 1 and FIG. 3 depicts a counter-clockwise rotating lawnmower blade 9. The primary difference between a clockwise rotating lawnmower blade 1 or 6 and a counter-clockwise rotating blade 9 is that the cutting edges 2 and 3 of a counter-clockwise rotating blade 9 are on the opposites sides of a clockwise rotating blade 1 or 6 as are the upturned ends 5. Counter-clockwise rotating mulching blades are also available similar to the mulching style blade 6 depicted in FIG. 2 but with the secondary cutting edges 7 and 8 on the opposite sides when compared to a clockwise rotating mulching blade 6.
Cutting grass is a very abrasive process. If a user starts with a lawnmower blade, sharpened properly and at the correct cutting angle, as they mow the lawn, the process of cutting grass quickly dulls the sharp cutting edges of the blade. As the cutting edges of the blade becomes duller and duller, instead of cutting the grass the blade starts to tear the grass. This not only leads to an unappealing lawn surface, but can damage the grass thereby increasing the grass' susceptibility to disease.
Consequently, there is a need to sharpen the lawnmower blade or blades on a regular basis. Professional lawn care providers often sharpen their lawnmower blades after every day's use. The same is often true for those individuals responsible for the care of lawns at golf courses and recreational areas such as playgrounds and parks. Individual home owners sharpen their lawnmower blades at their own discretion.
In re-sharpening a lawnmower blade, great care must be taken in a variety of areas. First and foremost is the need for safety. Regardless of the method of sharpening used, care should be taken to securely clamp or hold the lawnmower blade in place so that it does not come loose and injure someone or something. Secondly, if some form of powered sharpening mechanism is utilized, such as bench or disc grinders, there should be a means to trap and arrest any hot sparks resulting from the sharpening process in order to prevent burns or fires. Thirdly, it is important to retain the original angle of the cutting edges of both the primary, 2 and 3, and secondary, 7 and 8, cutting edges in order to maintain the proper grass cutting action. Fourth, when sharpening a lawnmower blade, it is important to maintain the balance of the blade. This means that in re-sharpening a lawnmower blade, all of the cutting edges on a given plane should have the same amount of material removed from them. If not, the high rotary speed of the blade in use can cause the grass to be cut unevenly leading to an unaesthetic appearance. Other areas where care is needed are well known in the art.
The means for re-sharpening a lawnmower blade are varied and numerous. In one method, a user clamps a lawnmower blade in a vice and utilizes a metal file to hand sharpen the blade. However, this can lead to erroneous and uneven cutting edge angles and cause the blade to become out of balance.
U.S. Pat. Pub. 2004/0142645 published on Jul. 22, 2004 to Harold Maus discloses a rotary lawnmower blade sharpener that can be utilized with a bench grinder to sharpen the primary cutting edges of a lawnmower blade. This sharpening device being distinguishable from the present invention in that there is no means provided for sharpening the secondary cutting surfaces of a mulching type blade as the fixture clamps the lawnmower blade about the center where the secondary cutting edges are located and does not allow the center of a mulching type blade to come in contact with the grinding wheel. In addition, the apparatus, as best understood and described, is only suitable for sharpening either clockwise rotating blades or counter-clockwise rotating blades but not both with the same apparatus.
U.S. Pat. Pub. 2004/0244538 published on Dec. 9, 2004 to Johannes Franzen, et al. discloses an apparatus for sharpening multiple blade knives. This sharpening device being distinguishable from the present invention in that there is no means provided for sharpening the secondary cutting surfaces of a mulching type blade as the fixture clamps the lawnmower blade about the center where the secondary cutting edges are located and does not allow the center of a mulching type blade to come in contact with the grinding wheel. In addition, the apparatus, as best understood and described, is only suitable for sharpening either clockwise rotating blades or counter-clockwise rotating blades, depending upon the relative position of the fixture to the grinding medium, but not both with the same apparatus.
U.S. Pat. No. 4,736,544 issued on Apr. 12, 1988 to Lawrence Greenquist discloses a blade holder for sharpening lawnmower blades. This sharpening device being distinguishable from the present invention in that there is no means provided for sharpening the secondary cutting surfaces of a mulching type blade as the fixture clamps the lawnmower blade about the center where the secondary cutting edges are located and does not allow the center of a mulching type blade to come in contact with the grinding wheel. As shown and described, the apparatus depicts the holder as being utilized to sharpen counter-clockwise rotating blades. In order to utilize the device to sharpen clockwise rotating blades, either the fixture or the grinding wheel must be physically removed and repositioned to the reverse side of the work bench which is a laborious and time consuming process.
U.S. Pat. No. 6,761,623 issued on Jul. 13, 2004 to Wayne Baker discloses an apparatus and method for sharpening blades at a predetermined angle. As disclosed, the blade is mounted on a clamping fixture above a disc grinder, the disc grinder being pivotally mounted at its base. This sharpening device, as best understood by the specifications and drawings, being distinguishable from the present invention in that there is no means provided for sharpening the secondary cutting surfaces of a mulching type blade. In addition, the apparatus is only suitable for sharpening either clockwise rotating blades or counter-clockwise rotating blades, depending upon the relative position of the fixture to the grinding medium, but not both with the same apparatus.
It is, therefore, an object of this invention to provide an apparatus and a method for sharpening both standard and mulching style lawnmower blades to the proper cutting edge angle.
It is a further object of this invention to provide an efficient and easy apparatus and method for sharpening both clockwise rotating lawnmower blades and counter-clockwise rotating lawnmower blades.
It is still a further object of this invention to assure the safety of the user and area by trapping and arresting any sparks generated during the process of re-sharpening a lawnmower blade for easy disposal later.
It is still a further object of this invention to make the process of loading, sharpening all cutting edges and unloading a quick, simple and accurate process for the user.
Other features and advantages of this disclosure will become apparent to one skilled in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included within the scope of the present invention.